1. Field of the Invention
The invention relates to method of formning a thin film in a semiconductor device, and more particularly, to method of forming a thin film in a semiconductor device capable of controlling the growth rate, thickness, density, and other material properties of the thin film.
2. Description of the Prior Art
As semiconductor devices are highly integrated, developments of processes of forming a thin film utilized in a semiconductor or a display device have been focused on processes for producing thinner films having more excellent material properties. To meet these circumstances, an atomic layer deposition method (hereinafter, referred to as an ALD method) has been highlighted. The ALD method has advantages that atomic layers can be uniformly deposited on wide substrates, the thickness of the thin film corresponding to repetition times of the process can be controlled, and step coverage is good (Applied Surface Science, 107, pp128 (1996), and Journal of the Electrochemical Society, 149(6), pp C306 (2002)). In addition, the atomic layer deposition process can be carried out below precursor dissociation temperature, so that a low-temperature process can be accommodated, and the process can be less sensitive to the process parameters such as temperature, pressure, etc. Furthermore, according to the ALD method, a thin film having excellent crystalline properties can be obtained.
However, the atomic layer deposition method has some disadvantages. For example, precursors and reaction gases have to be separately supplied. Furthermore, an additional purging step for cleaning the inside of a chamber is needed before supplying the precursors or the reaction gases to the chamber. Therefore, a process period may be extended because the above additional steps have to be repeated in every cycle until a desired thickness is obtained. In addition, a reaction rate between the precursor and the reaction gas needs to be increased to broaden a reaction temperature range because the temperature of reaction between the precursor and the reaction gas should be in a low temperature range.
In order to solve the above problems, an atomic layer deposition method together with a plasma applying method (hereinafter, referred to as a PEALD method) has been developed. Maintaining the advantages of the ALD method, the plasma enhanced atomic layer deposition method has additional advantages that a process period can be shortened due to improved deposition rate, and a process temperature range can be broadened due to improved reactivity of the reaction gas. Furthermore, the thin film with a higher density can be obtained.
According to several researches, it has been reported that, when the oxidized substance like Al2O3 is deposited in a temperature of 200xc2x0 C., the growth rate of the thin film deposited by the plasma enhanced atomic layer deposition method is 1.5 times higher than that of an atomic layer deposition method, and the density is also excellent. Other reports also have shown that, when the thin film comprising Ta2O5 is deposited, the plasma enhanced atomic layer deposition method provides higher dielectric constant and better electrical insulation properties than those of the conventional method (Electrochemical and Solid-state Letters, 4(7), pp F13(2001)).
While it is believed that differences in the growth rates or densities of the thin films are derived from the types of the deposition mechanism and the film deposition method.
It is an object of the present invention to provide a method of forming a thin film in a semiconductor device by alternately performing the ALD method and the PEALD method while adjusting the ratio of repetition times of the methods, so that the growth rate, density, and related material properties such as refraction index, dielectric constant, electric resistance, etc. can be estimated and controlled.
A method of forming a thin film in a semiconductor device according to an embodiment of the present invention comprises steps of: performing only one cycle of an atomic layer deposition method to form the thin film having a basic unit thickness on upper portion of a substrate; and performing only one cycle of a plasma enhanced atomic layer deposition method to form the thin film having the basic unit thickness on the upper portion of the substrate, wherein the steps are alternately repeated to form the thin film having a desired thickness.
In the aforementioned method, the ratio of repetition times of the atomic layer deposition method and the plasma enhanced atomic layer deposition method may be adjusted to be N:M, thereby controlling the growth rate and material properties of the thin film, where N and M are integer numbers.
In the aforementioned method, the plasma enhanced atomic layer deposition method and the atomic layer deposition method may use different precursors and different reaction gases as well as the same precursors and reaction gases.